The present invention relates generally to bicycles and, more particularly, to bicycle frame constructions wherein one or more members of the bicycle frame are joined together during manufacture.
The primary structural component of a conventional two-wheel bicycle is the frame. On a conventional road bicycle, the frame is typically constructed from a set of tubular members assembled together to form the frame. For many bicycles, the frame is constructed from members commonly referred to as the top tube, down tube, seat tube, seat stays and chain stays, and those members are joined together at intersections commonly referred to as the head tube, seat post, bottom bracket and rear dropout. As is commonly understood, it is occasionally more convenient to attach some of the members of the frame assembly to form subassemblies before the final assembly of all of the respective components.
The top tube usually extends from the head tube rearward to the seat tube. The head tube, sometimes referred to as the neck, is a short tubular structural member at the upper forward portion of the bicycle which supports the handlebar and front steering fork. The front wheel assembly is commonly supported between the legs of the front steering fork. The down tube usually extends downwardly and rearward from the head tube to the bottom bracket. The bottom bracket usually comprising a cylindrical member for supporting the pedals and chain drive mechanism which powers the bicycle. The seat tube usually extends from the bottom bracket upwardly to where it is joined to the rear end of the top tube. The seat tube also usually functions to telescopically receive a seat post for supporting a seat or saddle for the bicycle rider to sit on.
The chain stays normally extend rearward from the bottom bracket. The seat stays normally extend downwardly and rearward from the top of the seat tube. The chain stays and seat stays are normally joined together proximate a rear dropout and support the rear axle of the rear wheel assembly. Those skilled in the art will readily appreciate that the foregoing description represents one conventional construction of a bicycle frame. Many metal framed bicycles included one or more frame tubes that are simply welded together at designated locations. Those skilled in the art will also appreciate that the materials and material constructions associated with forming such a metal framed bicycle form a substantial portion of the overall weight of the resultant bicycle.
There is an ever present desire to reduce the weight of the bicycle frame so as to improve rider performance. Many manufacturers have recognized the use of carbon fiber materials as a viable lightweight replacement for metal based bicycle frame constructions. Still others have altered the composition of the metal based materials to achieve desired weight to strength ratios. Regardless of the material of the bicycle frame, one issue that remains problematic is the formation of the connection between the respective frame members.
Altering the shape and contour of the ends of the frame members alters the strength and performance of the bicycle frame. To provide the necessary structural integrity between the respective frame members, some manufacturers provide a connection wherein the respective frame members are secured together with extraneous connectors. Others form a wrapped joint wherein a wrapping material is wound about the interface of the ends of the respective frame members. Such methodologies complicate the assembly and manufacture processes and require supplemental connectors as well as skilled labor for forming and finishing such joints in a desired manner. Furthermore, such joint assemblies also present a weight penalty to the overall construction of the bicycle frame.
A joint construction having inadequate performance can lead to premature frame failure and/or undesired blemishes. During use, stresses supported by the frame of the bicycle are commonly concentrated at the jointed locations. Many joints have one joint member that is more rigid and/or capable of supporting a greater load than the other joint member. The construction of the respective ends of the joined members as well as the location of the joint with respect to the bicycle frame affect the ability of the respective ends to withstand the in-use load communicated across the joint. Commonly, inadequate joint constructions are evidenced by blemishes in the finish of the bicycle frame as the paint and/or other frame finishes crack or peel due to the non-uniform transmission of loads across the joint. Providing a unitary bicycle frame would resolve the issues associated with joint blemish and the increased weight associated with such frame joints however, such an approach would complicate the manufacturing processes associated with forming such a bicycle frame.
Therefore, there is a need for a bicycle frame joint system that does not unduly increase the weight of the resultant bicycle frame and which can tolerate the forces associated with operation of the bicycle in a manner that reduces incidents of finish blemishes. The present invention discloses such a bicycle frame joint system.